1. Field of the Invention
This invention relates to a method and apparatus for recognizing data traveling on a data transmission network by receiving, in a station of the network, identifiers. The identifiers each have a bit field for indicating if the identifiers belong to the reference identifiers attached to the station.
2. Discussion of the Background
A data transmission network, particularly in an industrial environment (a so-called ground network, for example) includes, in reference to FIG. 1, stations that are interconnected, through communication interfaces, by a transmission line 1 called a bus. Each of the stations transmits and receives on the network, data items; each data item constituting a field, i.e., an indivisible unit of bits. An identifier, a bit field or byte corresponding to each data item transmitted, allows the identification of the data item.
The identifier which is associated with each data item transmitted on the bus allows each station to determine if a particular data item is intended for the station. If it is intended for the station, information in the data item is given to that station. To perform these functions, each of the stations comprises a memory containing all of the identifiers which are associated with it.
Techniques for recognizing the identifiers are already known. A first known technique includes, at each station, a memory that can hold all the possible identifiers. By way of indication, this memory will have 2.sup.16 entries for 16-bit identifiers. It associates, with each identifier relating to the station, the address of the corresponding service specification. This technique exhibits the advantage of speed of recognition since the identifier itself constitutes the memory address, but the technique is restricting in memory space.
A second known technique performs a dichotomizing search in a table of identifiers grouping the identifiers recognized by the station, ranked by ascending order. The dichotomizing search determines by successive comparisons, in which half, then in which fourth, then in which eighth, then in which sixteenth, etc. the identifier is located. For a capacity of 2.sup.n identifiers, n dichotomizing search iterations must be performed. This technique exhibits the advantage of limiting the memory space but its identification time is too long to guarantee an acceptable performance (i.e., high speed performance).